Objective To determine the expression level of each gtf under different pH cultural conditions and to find the relationship between gtf expression levels with environmental pH in different strains of Streptococcus mutans （S.mutans）. Methods S.mutans form clinical isolation with different extracellular polysaccharides（EPS） producibility and UA159 were selected. Their ability to produce EPS under pH5.5 and pH7 were tested. Then in two strains, the relative quantity of gtfA, gtfB, gtfC, gtfD′ s mRNA which were related to S.mutan′ s ability to produce EPC, were examined by real-time reverse transcription-polymerase chain reaction（real-time RT-PCR） methods under different pH culture condition. Results At pH5.5, expression levels of gtfA, gtfB, gtfD were increased while that of gtfC were decreased in both strains, and that of gtfB, gtfC were higher in strain which produces more ECP. Conclusion The expression levels of gtfs related closely to the cariogenicity of S.mutan.
